The long-term objective of the proposed research is to understand binaural interaction and to apply this understanding to the problems of the hearing impaired. The proposed research, which is a direct outgrowth of previous work by the same investigators and includes substantial amounts of both psychophysical experimentation and theoretical modeling, is characterized by its concern with a broad range of binaural phenomena, its thrust toward the development of a unified quantitative theory that is consistent with physiological data, and its use of highly developed laboratory facilities and experimented techniques. In addition, the proposed research includes substantial work on impaired listeners as well as normal listeners. Study of impaired listeners is included both in order to gain further understanding of binaural interaction and in order to help alleviate the problems of the hearing impaired. During the proposed grant period, the theoretical research will proceed in two directions: (1) the development of hypothetical neural mechanisms that are consistent with available physiological data from the auditory nerve and the lateral and medial superior olives and (2) the development of psychoacoustic models that explicitly include a description of the information provided by the neural mechanisms. The predictions of the psychoacoustic models will be compared with results obtained for our experiments and from the literature. Our experimental research on normal listeners includes study of interaural intensity discrimination (with and without a roving level), the relations among various binaural unmasking), and adaptation to altered hearing. The experimental research on impaired listeners includes study of localization, lateralization, interaural discrimination, and detection of signals in noise. To the extent that this program is successful, it will provide a major improvement in our understanding of binaural interaction, and therefore, since binaural interaction plays a crucial role in auditory function, in our understanding of audition. Furthermore, insights that are gained concerning binaural interaction in impaired listeners will provide important background knowledge for later work on improved hearing aids and audiological evaluation procedures.